Why do all the aspens in one area turn the same color at the same time?

Answered by Amy Forman, Botanist and Ecologist, WAI ESER Program   www.idahoeser.com

We visited the mountains around Palisades reservoir and  noticed the aspen trees are turning color, but instead of all turning the same color, there were patches of trees turning orange and neighboring patches of trees turning yellow.  Why do all the aspens in one area turn the same color at the same time?

aspen1Great observation! Each patch of aspens is a genet, which is a group of organisms derived from the same seedling. All of the trees in one patch are part of the same organism. Aspens often reproduce by initiating new shoots off an existing mature root system-as anyone with aspens in their yard will certainly confirm! Because they share exactly the same genetic profile, they are all “programmed” to do the same thing at the same time. Some people like to think of all of the trees in one patch as clones. You can often differentiate one genet of trees from another the same way you can tell one person from another. We all have different skin, eye, and hair coloring based on the way our genes direct our bodies to assemble and distribute pigments. Trees also have different coloring based on the way their genes are expressed. As chlorophyll (the green pigment used for photosynthesis) is broken down and stored for the winter, other pigments such as aspen2carotenes (dark yellow/orange pigments) and xanthophylls (lighter yellow pigments) become more visible. Just as people with darker hair have more eumelanin than people with lighter hair, aspen genets with darker yellow leaves have more carotenes than genets with lighter yellow leaves.

The world’s largest and possibly oldest living organism is Pando, a Quaking Aspen clone in Utah.

Pando is believed to be the largest organism ever found at nearly 13 million pounds. The clone spreads over 106 acres, consisting of over 40,000 individual trees. Pando is named for the Latin word meaning “to spread”.

Leaf Parts
aspen3These are the basic parts of a leaf:

  • Petiole: This is the stalk which may attach the leaf to the stem; some leaves attach directly and don’t have petioles.
  • Blade: This is the main portion of the leaf. The cells of the blade, particularly those near the surface of the leaf, contain a high volume of chloroplasts, which carry out photosynthesis.
  • Midrib: This is the main vein which travels along the centre of the leaf and contains the phloem and xylem transport vessels.
  • Veins: Smaller veins veer off from the midrib to ensure that the transportation system of the plant extends to all parts of the leaf. The sections between the leaf veins are known as ‘inter-veinal’ areas.

Materials: Leaves, thin paper, crayons or oil pastels

  1. Collect leaves of various shapes and sizes.
  2. Place a leaf, bottom-side facing up, on a flat surface.
  3. Put a thin sheet of paper on top of the leaf.
  4. Rub the side of a crayon or an oil pastel gently on the area over the leaf. Observe as part of the leaf shape starts to appear.
  5. Continue until you’ve rubbed over the entire leaf.
  6. Remove the leaf from under the paper. Can you see all of the basic parts of the leaf on your rubbing?

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